CollectionView 横向滚动，自定义排序

无疑是重写flowlayout

import UIKit




class CustomFlowLayout: UICollectionViewFlowLayout {
    ///              行间距
    let RowSpace:CGFloat = 6
    ///                列间距
    let CollSpace:CGFloat = 6
    /// 每页每行多少列
    var numColl:Int = 4
    /// 每页行数
    var numRow:Int = 2
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    func getMyPageNum()->Int {
        if let collectionView = self.collectionView {
            
            let pageNums = self.numRow * self.numColl
            if let count = collectionView.dataSource?.collectionView(collectionView, numberOfItemsInSection: 0) {
                /// 余数
                let a = count%pageNums
                /// 商数
                let b = count/pageNums
                
                /// 页数
                var c:Int = b
                if a > 0 {
                    c = b + 1
                }
                
                
                return c
            }
            
            
            return 1
        }
        
        return 1
    }
    
    /// 内容大小
    override var collectionViewContentSize: CGSize{
        
        
        if let collectionView = self.collectionView {
            
            let page = self.getMyPageNum()
            let width:CGFloat = CGFloat(page) * collectionView.bounds.size.width
            
            return CGSize.init(width: width, height: collectionView.bounds.size.height)
        }
        
        return CGSize.zero
    }
    
    /// 自定义布局必须YES
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true
    }
    
    func getItemSize() -> CGSize {
        if let collectionView = self.collectionView {
            
            
            let itemW = (collectionView.bounds.size.width - CollSpace * CGFloat(self.numColl - 1)  )  / CGFloat(self.numColl)
            let itemH = (collectionView.bounds.size.height - RowSpace * CGFloat(self.numRow - 1)) / CGFloat(self.numRow)
            
            return CGSize.init(width: itemW, height: itemH)
        }
        
        
        
        return CGSize.init(width: 20, height: 20)
    }
    
    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        
        if let item = super.layoutAttributesForItem(at: indexPath) {
            
            if let collectionView = self.collectionView {
                
                
                
                let pageNums = self.numRow * self.numColl
                let itemW = self.getItemSize().width
                let itemH = self.getItemSize().height
                
            
                /// 页号 从零开始
                let c = indexPath.row/pageNums
                /// 余数
                let a = indexPath.row%pageNums
 
                
                
                var rect = item.frame
                rect.size.width = itemW
                rect.size.height = itemH
                rect.origin.x = CGFloat(a%self.numColl) * (itemW + CollSpace) + collectionView.bounds.size.width * CGFloat(c)
                let row = (indexPath.row/self.numColl)%self.numRow
                
                rect.origin.y = CGFloat(row) * (itemH + RowSpace)
                
                
                print("rect=== \(rect)  \(indexPath.row)")
                
                item.frame = rect
            }
            
            
            return item
            
        }
        

        
        return nil
    }
    
    override func prepare() {
        
        
        super.prepare()
        self.scrollDirection = .horizontal
        
        self.itemSize = self.getItemSize()
        self.sectionInset = .zero
        self.minimumLineSpacing = self.RowSpace
        self.minimumInteritemSpacing = self.CollSpace
        
    }
    
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        
        if let array = super.layoutAttributesForElements(in: rect) {
            var attributes:[UICollectionViewLayoutAttributes] = [UICollectionViewLayoutAttributes]();
            for (index,item) in array.enumerated() {
                
                if let model  = self.layoutAttributesForItem(at: item.indexPath) {
                    attributes.append(model)
                }
            }
            
            return attributes
        }


        return nil
    }
    
}